When in the medical field a patient has a cerebral or cardiac vascular injury, it is necessary to check the viscosity of the blood because this parameter plays an important role in the diagnosis of the vascular injury and in the determination of an appropriate treatment, for example a treatment on the basis of blood thinning medication. In order to determine the viscosity of the blood at present it is necessary to perform measurements on blood samples taken from the patient. This procedure has significant drawbacks. The result of the measurements is not immediately available and the taking of the blood samples itself is invasive and hence potentially contaminating. It is a further drawback that the taking of the blood samples must be periodically repeated so as to check the effect of the treatment; this could damage the vessels of the patient. No alternative for this method of determining the viscosity of blood is known at present. An invasive means is to be understood to mean herein the taking of a blood sample which necessitates, for example the introduction of a needle into the blood vessel so as to fill a syringe with a blood sample.
Patent EP 0 430 374 (U.S. Pat. No. 5,103,826, Bonnefous, Apr. 14, 1992) already discloses an ultrasonic echography apparatus which is provided with a system for the processing of ultrasonic signals in order to determine speed profiles of the blood in an artery. The echography apparatus includes a transducer which emits and receives ultrasonic signals from the region of an artery of a patient, and a transmitter stage which is connected to the probe. The processing system estimates the speed of the blood in the artery as a function of time and scanning depth while utilizing a method for the correlation of successive signals returned by the transducer.